Visible-light-responsive photoactive coating, coated article, and method of making same

ABSTRACT

A method is provided for forming a photoactive coating having a photoabsorption band in the visible region of the electromagnetic spectrum. The method includes depositing a precursor composition over at least a portion of a float glass ribbon in a molten metal bath by a CVD coating device. The precursor composition includes a titania precursor material and at least one other precursor material selected from chromium (Cr), vanadium (V), manganese (Mn), copper (Cu), iron (Fe), magnesium (Mg), scandium (Sc), yttrium (Y), niobium (Nb), molybdenum (Mo), ruthenium (Ru), tungsten (W), silver (Ag), lead (Pb), nickel (Ni), rhenium (Re), and mixtures thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.10/193,446, filed Jul. 11, 2002 now U.S. Pat. No. 7,096,692, which is acontinuation-in-part of U.S. application Ser. No. 10/075,316 toGreenberg et al., entitled “Photocatalytically-Activated Self-CleaningAppliances”, filed Feb. 14, 2002 now U.S. Pat. No. 6,722,159, which is adivisional of U.S. application Ser. No. 09/282,943 filed Apr. 1, 1999(now U.S. Pat. No. 6,413,581), which is a divisional of U.S. applicationSer. No. 08/899,257, filed Jul. 23, 1997 (now U.S. Pat. No. 6,027,766),which claimed the benefit of U.S. Provisional Application Ser. No.60/040,566, filed Mar. 14, 1997, all of which applications are hereinincorporated by reference in their entirety. This application alsoclaims the benefit of U.S. Provisional Application Ser. No. 60/305,057filed Jul. 13, 2001, which is herein incorporated by reference in itsentirety.

FIELD OF THE INVENTION

The present invention relates to methods of depositing photoactivecoatings on a substrate (e.g., a glass sheet or a continuous float glassribbon), to methods of making photocatalytic and/or hydrophilic coatingsthat exhibit photoactivity upon irradiation with visible light, and toarticles of manufacture prepared according to the methods.

TECHNICAL CONSIDERATIONS

For many substrates, e.g., glass substrates such as architecturalwindows, automotive transparencies, and aircraft windows, it isdesirable for good visibility that the surface of the substrate issubstantially free of surface contaminants, such as common organic andinorganic surface contaminants, for as long a duration as possible.Traditionally, this has meant that these surfaces are cleanedfrequently. This cleaning operation is typically performed by manuallywiping the surface with or without the aid of chemical cleaningsolutions. This approach can be labor, time, and/or cost intensive.Therefore, a need exists for substrates, particularly glass substrates,having surfaces that are easier to clean than existing glass substratesand which reduce the need or frequency for such manual cleaning.

It is known that some semiconductor metal oxides can provide aphotoactive (hereinafter “PA”) coating. The terms “photoactive” or“photoactively” refer to the photogeneration of a hole-electron pairwhen illuminated by radiation of a particular frequency, usuallyultraviolet (“UV”) light. Above a certain minimum thickness, these PAcoatings are typically photocatalytic (hereinafter “PC”). By“photocatalytic” is meant a coating having self-cleaning properties,i.e., a coating which upon exposure to certain electromagneticradiation, such as UV, interacts with organic contaminants on thecoating surface to degrade or decompose the organic contaminants. Inaddition to their self-cleaning properties, these PC coatings are alsotypically hydrophilic, i.e. water wetting with a contact angle withwater of generally less than 20 degrees. The hydrophilicity of the PCcoatings helps reduce fogging, i.e. the accumulation of water dropletson the coating, which fogging can decrease visible light transmissionand visibility through the coated substrate.

A problem with these conventional PC coatings is that they typicallyexhibit photoactivity or photocatalysis only upon exposure toultraviolet (UV) light in wavelengths shorter than about 380 nanometers(nm). This means that the PC coatings make use of only about 3% to 5% ofthe solar energy that reaches the earth, which can necessitate the useof a UV light source (such as a conventional mercury or black lamp) inorder to provide sufficient energy for photocatalysis.

In order to address this problem, attempts have been made to modifyconventional PC coatings to shift the photoabsorption band of thecoating material from the UV region into the visible region (400 nm to800 nm) of the electromagnetic spectrum. For example, U.S. Pat. No.6,077,492 to Anpo et al. discloses a method of shifting thephotoabsorption band of titanium oxide photocatalysts from the UV regioninto the visible light region by high-energy ion implantation ofselected metal ions into the photocatalyst. Subsequent investigation ofthis ion implantation method has determined that the photoabsorptionband shift into the visible region requires not only high-energy ionimplantation but also calcination in oxygen of the metal ion-implantedtitanium oxide (Use Of Visible Light. Second-Generation Titanium OxidePhotocatalysts Prepared By The Application Of An Advanced MetalIon-Implantation Method, M. Anpo, Pure Appl. Chem., Vol. 72, No. 9, pp.1787-1792 (2000)). EP 1,066,878 discloses a sol-gel method of dopingtitania with minute amounts of selected metal ions to shift thephotoabsorption band of the titania into the visible region.

However, these ion implantation and sol-gel coating methods are noteconomically or practically compatible with certain applicationconditions or substrates. For example, in a conventional float glassprocess, the float glass ribbon in the molten metal bath can be too hotto accept the sol due to evaporation or chemical reaction of the solventused in the sol. Conversely, when the sol is applied to substrates thatare below a specific temperature for the formation of crystalline formsof the catalyst, the sol-coated substrates are reheated. Reheating to atemperature sufficient to calcinate the coating or form the crystallizedphotocatalyst can require a substantial investment in equipment, energy,and handling costs, and can significantly decrease productionefficiency. Further, reheating a sodium containing substrate, such assoda-lime-silica glass, to a temperature sufficient to calcinate thecoating increases the opportunity for sodium ions in the substrate tomigrate into the coating. This migration can result in what isconventionally referred to as “sodium ion poisoning” of the depositedcoating. The presence of these sodium ions can reduce or destroy thephotocatalytic activity of the PC coating. Moreover, theion-implantation and sol-gel methods typically result in thick coatings,e.g., several microns thick, which may have an adverse effect on theoptical and/or aesthetic properties of coated articles.

Typically, as the thickness of the PC coating increases, the lighttransmittance and the reflectance of the coating go through a series ofminimums and maximums due to optical interference effects. The reflectedand transmitted color of the coating also varies due to these opticaleffects. Thus, coatings thick enough to provide the desiredself-cleaning properties can have undesirable optical characteristics.

Therefore, it would be advantageous to provide a method of making a PAcoating with photoabsorption in the visible region that is compatiblewith a conventional float glass process and/or an article made inaccordance with the method which reduce or eliminate at least some ofthe above-described drawbacks.

SUMMARY OF THE INVENTION

A method is provided for forming a coating by depositing a precursorcomposition over at least a portion of a substrate surface by a CVDcoating device. The precursor composition includes a photoactive coatingprecursor material, such as a metal oxide or semiconductor metal oxideprecursor material, and a photoabsorption band modifying precursormaterial. In one embodiment, the coating is deposited over a float glassribbon in a molten metal bath. In another embodiment, the coating isdeposited over a float glass ribbon after exiting the molten metal bathbut prior to entering a heat treatment device, such as an annealinglehr. The resultant coating is one that results in at leasthydrophilicity, e.g., photoactive hydrophilicity, of a coating on asubstrate and can also result in photocatalytic activity sufficient tobe a photocatalytic coating.

Another method of forming a photoactive coating having a photoabsorptionband in the visible region of the electromagnetic spectrum includesdepositing a precursor composition over at least a portion of a floatglass ribbon in a molten metal bath by a CVD coating device. Theprecursor composition includes at least one titania precursor material.In one embodiment, the titania precursor material includes titanium andoxygen, e.g., an alkoxide, such as but not limited to titaniummethoxides, ethoxides, propoxides, butoxides, and the like or isomersthereof, such as but not limited to titanium isopropoxide,tetraethoxide, and the like. In another embodiment, the titaniaprecursor material comprises titanium tetrachloride. The precursorcomposition also includes at least one other precursor material having ametal selected from chromium (Cr), vanadium (V), manganese (Mn), copper(Cu), iron (Fe), magnesium (Mg), scandium (Sc), yttrium (Y), niobium(Nb), molybdenum (Mo), ruthenium (Ru), tungsten (W), silver (Ag), lead(Pb), nickel (Ni), rhenium (Re), or any mixtures or combinationscontaining one or more thereof. In one embodiment, the other precursormaterial can be an oxide, alkoxide, or mixtures thereof. All root meansquare roughness values are those determinable by atomic forcemicroscopy by measurement of the root mean square (RMS) roughness over asurface area of one square micrometer. Additionally, any reference“incorporated herein” is to be understood as being incorporated in itsentirety.

An additional method of the invention includes depositing a sodium iondiffusion barrier layer over at least a portion of a substrate,depositing a photoactive coating over the barrier layer, and implantingone or more selected metal ions into the photoactive coating byion-implantation to form a photoactive coating having an absorption bandincluding at least one wavelength in the range of 400 nm to 800 nm.

An article of the invention includes a substrate having at least onesurface and a coating deposited over at least a portion of the substratesurface. The coating includes a photoactive coating material, such astitania, and at least one additional material selected from chromium(Cr), vanadium (V), manganese (Mn), copper (Cu), iron (Fe), magnesium(Mg), scandium (Sc), yttrium (Y), niobium (Nb), molybdenum (Mo),ruthenium (Ru), tungsten (W), silver (Ag), lead (Pb), nickel (Ni),rhenium (Re), or any mixtures or combinations containing one or morethereof. In one embodiment, the coating is deposited over the substrateby chemical vapor deposition.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view (not to scale) of a portion of a substratehaving a photoactive coating of the invention deposited thereon;

FIG. 2 is a side view (not to scale) of a coating process for applying aphotoactive metal oxide coating of the invention onto a glass ribbon ina molten metal bath for a float glass process; and

FIG. 3 is a side view (not to scale) of an insulating glass unitincorporating features of the invention.

DESCRIPTION OF THE INVENTION

As used herein, spatial or directional terms, such as “inner”, “outer”,“above”, “below”, “top”, “bottom”, and the like, relate to the inventionas it is shown in the drawing figures. However, it is to be understoodthat the invention can assume various alternative orientations and,accordingly, such terms are not to be considered as limiting. Further,all numbers expressing dimensions, physical characteristics, processingparameters, quantities of ingredients, reaction conditions, and the likeused in the specification and claims are to be understood as beingmodified in all instances by the term “about”. Accordingly, unlessindicated to the contrary, the numerical values set forth in thefollowing specification and claims are approximations that can varydepending upon the desired properties sought to be obtained by thepresent invention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical value should at least be construed in light of the numberof reported significant digits and by applying ordinary roundingtechniques. Moreover, all ranges disclosed herein are to be understoodto encompass any and all subranges subsumed therein. For example, astated range of “1 to 10” should be considered to include any and allsubranges between (and inclusive of) the minimum value of 1 and themaximum value of 10; that is, all subranges beginning with a minimumvalue of 1 or more and ending with a maximum value of 10 or less, e.g.,5.5 to 10. Further, as used herein, the terms “deposited over” or“provided over” mean deposited or provided on but not necessarily insurface contact with. For example, a coating “deposited over” asubstrate does not preclude the presence of one or more other coatingfilms of the same or different composition located between the depositedcoating and the substrate. Additionally, all percentages disclosedherein are “by weight” unless indicated to the contrary. All root meansquare roughness values are those determinable by atomic forcemicroscopy by measurement of the root mean square (RMS) roughness over asurface area of one square micrometer. Additionally, all references“incorporated by reference” herein are to be understood as beingincorporated in their entirety.

Referring now to FIG. 1, there is shown an article 20 having features ofthe present invention. The article 20 includes a substrate 22 having afirst surface 21 and a second surface 60. The substrate 22 is notlimiting to the invention and can be of any desired material having anydesired characteristics, such as opaque or transparent substrates. By“transparent” is meant having a visible light transmittance of greaterthan 0% to 100%. By “opaque” is meant having a visible lighttransmittance of 0%. By “visible light” is meant electromagnetic energyhaving a wavelength in the range of 400 nanometers (nm) to 800 nm.Examples of suitable substrates include, but are not limited to, plasticsubstrates (such as polyacrylates, polycarbonates, andpolyethyleneterephthalate (PET)); metal substrates; enameled or ceramicsubstrates; glass substrates; or mixtures or combinations thereof. Forexample, the substrate can be conventional untintedsoda-lime-silica-glass, i.e. “clear glass”, or can be tinted orotherwise colored glass, borosilicate glass, leaded glass, tempered,untempered, annealed, or heat strengthened glass. The glass can be ofany, type, such as conventional float glass, flat glass, or a floatglass ribbon, and can be of any composition having any opticalproperties, e.g., any value of visible transmission, ultraviolettransmission, infrared transmission, and/or total solar energytransmission. Types of glass suitable for the practice of the inventionare described, for example but not to be considered as limiting, in U.S.Pat. Nos. 4,746,347; 4,792,536; 5,240,886; 5,385,872; and 5,393,593. Forexample, the substrate 22 can be a float glass ribbon, a glass pane ofan architectural window, a skylight, one pane of an insulating glassunit, a mirror, a shower door, glass furniture (e.g., glass tabletops,glass cabinets, etc.) or a ply for a conventional automotive windshield,side or back window, sun roof, or an aircraft transparency, just to namea few.

A photoactively-modified (hereinafter “PM”) coating 24 of the inventioncan be deposited over at least a portion of the substrate 22, e.g., overall or a portion of a major surface of the substrate 22, such as overall or a portion of the surface 21 or the surface 60. In the illustratedembodiment, the PM coating 24 is shown on the surface 21. As usedherein, the term “photoactively modified” refers to a material orcoating which is photoactive and which includes at least one additive ordopant that acts to shift and/or widen the photoabsorption band of thematerial compared to that of the material without the additive. By“photoabsorption band” is meant the range of electromagnetic radiationabsorbed by a material to render the material photoactive. The PMcoating 24 can be photocatalytic, photoactively hydrophilic, or both. By“photoactively hydrophilic” is meant a coating in which the contactangle of a water droplet on the coating decreases with time as a resultof exposure of the coating to electromagnetic radiation in thephotoabsorption band of the material. For example, the contact angle candecrease to a value less than 15°, such as less than 10°, and can becomesuperhydrophilic, e.g., decrease to less than 5°, after sixty minutes ofexposure to radiation in the photoabsorption band of the material havingan intensity of 24 W/m² at the PM coating surface. Although photoactive,the coating 24 may not necessarily be photocatalytic to the extent thatit is self-cleaning, i.e., may not be sufficiently photocatalytic todecompose organic material like grime on the coating surface in areasonable or economically useful period of time.

The PM coating 24 of the invention includes (1) a photoactive coatingmaterial and (2) an additive or dopant configured to widen or shift thephotoabsorption band of the coating compared to that of the coatingwithout the dopant material. The photoactive coating material (1)includes at least one metal oxide, such as but not limited to, one ormore metal oxides or semiconductor metal oxides, such as titaniumoxides, silicon oxides, aluminum oxides, iron oxides, silver oxides,cobalt oxides, chromium oxides, copper oxides, tungsten oxides, zincoxides, zinc/tin oxides, strontium titanate, and mixtures thereof. Themetal oxide can include oxides, super-oxides or sub-oxides of the metal.The metal oxide can be crystalline or at least partially crystalline. Inone exemplary coating of the invention, the photoactive coating materialis titanium dioxide. Titanium dioxide exists in an amorphous form andthree crystalline forms, i.e., the anatase, rutile and brookitecrystalline forms. The anatase phase titanium dioxide is particularlyuseful because it exhibits strong photoactivity while also possessingexcellent resistance to chemical attack and excellent physicaldurability. However, the rutile phase or combinations of the anataseand/or rutile phases with the brookite and/or amorphous phases are alsoacceptable for the present invention.

The photoabsorption band widening or shifting material (2) can be anymaterial that widens or shifts the photoabsorption band of the resultantcoating to extend at least partly into, or extend further into, thevisible region of the spectrum (i.e., widens or shifts thephotoabsorption band to include at least one wavelength in the range of400 nm to 800 nm not in the photoabsorption band of the coating withoutthe dopant material (2)). In one exemplary embodiment, the material (2)includes at least one of chromium (Cr), vanadium (V), manganese (Mn),copper (Cu), iron (Fe), magnesium (Mg), scandium (Sc), yttrium (Y),niobium (Nb), molybdenum (Mo), ruthenium (Ru), tungsten (W), silver(Ag), lead (Pb), nickel (Ni), rhenium (Re), or any mixtures orcombinations containing any one or more thereof. The material (2) ispresent in the PM coating 24 in an amount sufficient to widen or shiftthe photoabsorption band of the coating 24 to extend at least partlyinto, or extend further into, the visible region without adverselyimpacting the desired coating performance, e.g., reflectivity,transmittance, color, etc. Additionally, in the practice of theinvention, the material (2) does not necessarily have to be concentratedat or near the coating surface 21 but, rather, can be deposited in sucha manner that it is dispersed or incorporated into the bulk of thecoating 24.

The PM coating 24 should be sufficiently thick so as to provide anacceptable level of photoactivity, e.g., photocatalytic activity and/orphotoactive hydrophilicity, for a desired purpose. There is no absolutevalue which renders the PM coating 24 “acceptable” or “unacceptable”because whether a PM coating 24 has an acceptable level of photoactivityvaries depending largely on the purpose and conditions under which thePM coated article is being used and the performance standards selectedto match that purpose. However, the thickness of the PM coating 24 toachieve photoactive hydrophilicity can be much less than is needed toachieve a commercially acceptable level of photocatalytic self-cleaningactivity. For example, in one embodiment the PM coating 24 can have athickness in the range of 10 Å to 5000 Å, where thicker coatings in thisrange can have photocatalytic self-cleaning activity for at least someperiod of time as well as hydrophilicity. As the coatings get thinner inthis range, photocatalytic self-cleaning activity typically decreases inrelation to performance and/or duration. As coating thickness decreasesin such ranges as 50 Å to 3000 Å, e.g., 100 Å to 1000 Å, e.g., 200 Å to600 Å, e.g., 200 Å to 300 Å, photocatalytic self-cleaning activity maybe immeasurable but photoactive hydrophilicity can still be present inthe presence of selected electromagnetic radiation, e.g., within thephotoabsorption band of the material.

In another aspect of the invention, the outer surface 25 of the PMcoating 24 of the invention can be much smoother than previousself-cleaning coatings while still maintaining its photoactivehydrophilicity and/or photocatalytic activity. For example, the PMcoating 24, in particular the top or outer surface 25 of the coating,can have an RMS surface roughness of less than 5 nm even for thincoatings in the above ranges, such as 200 Å to 300 Å, e.g., less than4.9 nm, e.g., less than 4 nm, e.g., less than 3 nm, e.g., less than 2nm, e.g., less than 1 nm e.g., 0.3 nm to 0.7 nm.

In a still further aspect of the invention, the PM coating 24 can bemade denser than previous hydrophilic, self-cleaning coatings. Forexample, the PM coating 24 can be substantially non-porous. By“substantially non-porous” is meant that the coating is sufficientlydense that the coating can withstand a conventional hydrofluoric acidtest in which a drop of 0.5 weight percent (wt. %) aqueous hydrofluoricacid (HF) solution is placed on the coating and covered with a watchglass for 8 minutes (mins) at room temperature. The HF is then rinsedoff and the coating visually examined for damage. An alternative HFimmersion test is described in Industrial Engineering Chemistry &Research, Vol. 40, No. 1, page 26, 2001 by Charles Greenberg, hereinincorporated by reference. The denser PM coating 24 of the inventionprovides more protection to the underlying substrate against chemicalattack than previous more porous self-cleaning coatings and also isharder and more scratch resistant than previous sol-gel appliedself-cleaning coatings.

The PM coating 24 can be deposited directly on, i.e., in surface contactwith, the surface 21 of the substrate 22 as shown in FIG. 1. Even with asodium-containing substrate, such as soda-lime-silica glass, thin PMcoatings 24 of the invention, e.g., less than 1000 Å, should not berendered non-photoactive by sodium in the substrate when the coating isapplied by the in-bath method described below. Therefore, an easier toclean soda-lime-silica glass can be made without a sodium barrier layerbetween the glass and the PM coating 24 of the invention. Optionally,such a barrier layer could be used.

Alternatively, one or more other layers or coatings can be interposedbetween the PM coating 24 and the substrate 22. For example, the PMcoating 24 can be an outer or the outermost layer of a multilayer stackof coatings present on substrate 22 or the PM coating 24 can be embeddedas one of the layers other than the outermost layer within such amulti-layer stack. By “an outer layer” is meant a layer receivingsufficient exciting electromagnetic radiation, e.g., radiation withinthe photoabsorption band of the layer material, to provide the coatingwith sufficient photoactivity to be at least photoactively hydrophilicif not necessarily photocatalytic. In one embodiment, the PM coating 24is the outermost coating on the substrate 22.

A PM coating 24 of the invention can be formed on the substrate 22 byany conventional method, such as ion-implantation, spray pyrolysis,chemical vapor deposition (CVD), or magnetron sputtered vacuumdeposition (MSVD). In the ion-implantation method, metal ions areimplanted into the coating by high voltage acceleration. In the spraypyrolysis method, an organic or metal-containing precursor compositionhaving (1) a metal oxide precursor material, e.g., a titania precursormaterial, and (2) at least one photoabsorption band modifying precursormaterial, i.e., a dopant material (such as an organometallic precursormaterial), is carried in an aqueous suspension, e.g. an aqueoussolution, and is directed toward the surface of the substrate 22 whilethe substrate 22 is at a temperature high enough to cause the precursorcomposition to decompose and to form a PM coating 24 on the substrate22. In a CVD method, the precursor composition is carried in a carriergas, e.g., nitrogen gas, and directed toward the substrate 22. In theMSVD method, one or more metal-containing cathode targets are sputteredunder reduced pressure in an inert or oxygen-containing atmosphere todeposit a sputter coating over substrate 22. The substrate 22 can beheated during or after coating to cause crystallization of the sputtercoating to form the PM coating 24. For example, one cathode can besputtered to provide the metal oxide precursor material (1) and anothercathode can be sputtered to provide the dopant material (2).Alternatively, a single cathode already doped with the desired dopantmaterial can be sputtered to form the PM coating 24.

Each of the methods has advantages and limitations depending upon thedesired characteristics of the PM coating 24 and the type of glassfabrication process. For example, in a conventional float glass processmolten glass is poured onto a pool of molten metal, e.g., tin, in amolten metal (tin) bath to form a continuous float glass ribbon.Temperatures of the float glass ribbon in the tin bath generally rangefrom 1203° C. (2200° F.) at the delivery end of the bath to 592° C.(1100° F.) at the exit end of the bath. The float glass ribbon isremoved from the tin bath and annealed, i.e. controllably cooled, in alehr before being cut into glass sheets of desired length and width. Thetemperature of the float glass ribbon between the tin bath and theannealing lehr is generally in the range of 480° C. (896° F.) to 580° C.(1076° F.) and the temperature of the float glass ribbon in theannealing lehr generally ranges from 204° C. (400° F.) to 557° C. (1035°F.) peak. U.S. Pat. Nos. 4,466,562 and 4,671,155 (hereby incorporated byreference) provide a discussion of the float glass process.

The CVD and spray pyrolysis methods may be preferred over the MSVDmethod in a float glass process because they are more compatible withcoating continuous substrates, such as float glass ribbons, at elevatedtemperatures. Exemplary CVD and spray pyrolysis coating methods aredescribed in U.S. Pat. Nos. 4,344,986; 4,393,095; 4,400,412; 4,719,126;4,853,257; and 4,971,843, which patents are hereby incorporated byreference.

In the practice of the invention, one or more CVD coating apparatus canbe employed at several points in the float glass ribbon manufacturingprocess. For example, CVD coating apparatus may be employed as the floatglass ribbon travels through the tin bath, after it exits the tin bath,before it enters the annealing lehr, as it travels through the annealinglehr, or after it exits the annealing lehr. Because the CVD method cancoat a moving float glass ribbon yet withstand the harsh environmentsassociated with manufacturing the float glass ribbon, the CVD method isparticularly well suited to provide the PM coating 24 on the float glassribbon in the molten tin bath. U.S. Pat. Nos. 4,853,257; 4,971,843;5,536,718; 5,464,657; 5,714,199; and 5,599,387, hereby incorporated byreference, describe CVD coating apparatus and methods that can be usedin the practice of the invention to coat a float glass ribbon in amolten tin bath.

For example, as shown in FIG. 2, one or more CVD coaters 50 can belocated in the tin bath 52 above the molten tin pool 54. As the floatglass ribbon 56 moves through the tin bath 52, the vaporized precursorcomposition (i.e., the photoactive coating precursor material (1), e.g.,metal oxide precursor material, and the photoabsorption band modifyingmaterial (2), e.g., an organometallic precursor material), can be addedto a carrier gas and directed onto the top surface 21 of the ribbon 56.The precursor composition decomposes to form a PM coating 24 of theinvention. The material (2) can be at least partially soluble in thecoating precursor material (1), such as fully soluble in the coatingprecursor material (1) under the desired deposition conditions. Anydesired amount of the material (2) to achieve a desired shift of thephotoabsorption band into the visible region can be added to, mixedinto, or solubilized in the coating precursor material (1).Alternatively, the two separate precursors can be separately vaporizedand combined.

Exemplary coating precursor materials (1) (e.g., titania precursormaterials) that can be used in the practice of the present invention toform titanium dioxide PM coatings 24 by the CVD method include, but arenot limited to, oxides, sub-oxides, or super-oxides of titanium. In oneembodiment, the precursor material (1) can include one or more titaniumalkoxides, such as but not limited to titanium methoxide, ethoxide,propoxide, butoxide, and the like; or isomers thereof, e.g., titaniumisopropoxide, tetraethoxide, and the like. Exemplary precursor materialsuitable for the practice of the invention include, but are not limitedto, titanium tetraisopropoxide (Ti(OC₃H₇)₄) (hereinafter “TTIP”) andtitanium tetraethoxide (Ti(OC₂H₅)₄) (hereinafter “TTEt”). Alternatively,the titania precursor material (1) can be titanium tetrachloride.

The photoabsorption band shifting material (2) can be any material thatshifts or widens the photoabsorption band of the resultant coating toextend at least partly into, or extend further into, the visible region(400 nm to 800 nm) of the electromagnetic spectrum. The material caninclude one or more of chromium (Cr), vanadium (V), manganese (Mn),copper (Cu), iron (Fe), magnesium (Mg), scandium (Sc), yttrium (Y),niobium (Nb), molybdenum (Mo), ruthenium (Ru), tungsten (W), silver(Ag), lead (Pb), nickel (Ni), rhenium (Re), and/or any mixtures orcombinations thereof. For example, the precursor material (2) can be ametal oxide or alkoxide. In one embodiment, the material (2) is at leastpartially soluble, e.g., mostly soluble, in the precursor material (1).Exemplary carrier gases that can be used in the CVD method of theinvention include but are not limited to air, nitrogen, oxygen, ammoniaand mixtures thereof. The concentration of the precursor composition inthe carrier gas can vary depending upon the specific precursorcomposition used. However, it is anticipated that for coatings having athickness of about 200 Å, the concentration of precursor composition inthe carrier gas will typically be in the range of 0.01 volume % to 0.1volume %, e.g., 0.01 volume % to 0.06 volume %, e.g., 0.015 volume % to0.06 volume %; e.g., 0.019 volume % to 0.054 volume %. For thickercoatings, the precursor compositions can be higher.

For the CVD method (as well as the spray pyrolysis method discussedbelow), the temperature of the substrate 22 (such as a float glassribbon 56) during formation of the PM coating 24 thereon should bewithin the range which will cause the metal containing precursorcomposition to decompose and form a coating having a desired amount ofphotoactivity, e.g., photocatalytic activity, photoactivehydrophilicity, or both. The lower limit of this temperature range islargely affected by the decomposition temperature of the selectedprecursor composition. For the above listed titanium-containingprecursors, the lower temperature limit of the substrate 22 to providesufficient decomposition of the precursor composition is generally inthe range of 400° C. (752° F.) to 500° C. (932° F.). The upper limit ofthis temperature range can be affected by the method of coating thesubstrate. For example, where the substrate 22 is a float glass ribbon56 and the PM coating 24 is applied to the float glass ribbon 56 in themolten tin bath 50 during manufacture of the float glass ribbon 56, thefloat glass ribbon 56 can reach temperatures in excess of 1000° C.(1832° F.). The float glass ribbon 56 can be attenuated or sized (e.g.stretched or compressed) at temperatures above 800° C. (1472° F.). Ifthe PM coating 24 is applied to the float glass ribbon 56 before orduring attenuation, the PM coating 24 can crack or crinkle as the floatglass ribbon 56 is stretched or compressed respectively. Therefore, thePM coating 24 can be applied when the float glass ribbon 56 isdimensionally stable (except for thermal contraction with cooling),e.g., below 800° C. (1472° F.) for soda lime silica glass, and the floatglass ribbon 56 is at a temperature to decompose the metal-containingprecursor, e.g., above 400° C. (752° F.).

For spray pyrolysis, U.S. Pat. Nos. 4,719,126; 4,719,127; 4,111,150; and3,660,061, herein incorporated by reference, describe spray pyrolysisapparatus and methods that can be used with a conventional float glassribbon manufacturing process. While the spray pyrolysis method like theCVD method is well suited for coating a moving float glass ribbon, thespray pyrolysis has more complex equipment than the CVD equipment and isusually employed between the exit end of the tin bath and the entranceend of the annealing lehr.

Exemplary metal-containing precursor compositions that can be used inthe practice of the invention to form PM coatings by the spray pyrolysismethod include relatively water insoluble organometallic reactants,specifically metal acetylacetonate compounds, which are jet milled orwet ground to a particle size of less than 10 microns and suspended inan aqueous medium by the use of a chemical wetting agent. A suitablemetal acetylacetonate precursor material to form a titanium dioxidecontaining PM coating is titanyl acetylacetonate (TiO(C₅H₇O₂) ₂). Aphotoabsorption band modifying material, such as described above, can bemixed with or solubilized into the acetylacetonate precursor material.In one embodiment, the relative concentration of the metalacetylacetonate and band shifting precursor materials in the aqueoussuspension ranges from 5 to 40 weight percent of the aqueous suspension.The wetting agent can be any relatively low foaming surfactant,including anionic, nonionic or cationic compositions. In one embodiment,the surfactant is nonionic. The wetting agent is typically added at0.24% by weight, but can range from 0.01% to 1% or more. The aqueousmedium can be distilled or deionized water. Aqueous suspensions forpyrolytic deposition of metal-containing films are described in U.S.Pat. No. 4,719,127 particularly at column 2, line 16, to column 4, line48, which is herein incorporated herein by reference.

As will be appreciated by those skilled in the art, the bottom surface60 of the float glass ribbon resting directly on the molten tin(commonly referred to as the “tin side”) has diffused tin in the surfacewhich provides the tin side with a pattern of tin absorption that isdifferent from the opposing surface 21 not in contact with the moltentin (commonly referred to as “the air side”). The PM coating of theinvention can be formed on the air side of the float glass ribbon whileit is supported on the tin by the CVD method as described above, on theair side of the float glass ribbon after it leaves the tin bath byeither the CVD or spray pyrolysis methods, and/or on the tin side of thefloat glass ribbon after it exits the tin bath by the CVD method.

As an alternative to including oxygen in the atmosphere of the tin bathto form oxide coatings, the precursor composition can itself include oneor more sources of organic oxygen. The organic oxygen can be, forexample, an ester or carboxylate ester, such as an alkyl ester having analkyl group with a β-hydrogen. Suitable esters can be alkyl estershaving a C₂ to C₁₀ alkyl group. Exemplary esters which can be used inthe practice of the invention are described in WO 00/75087, hereinincorporated by reference.

With respect to MSVD, U.S. Pat. Nos. 4,379,040; 4,861,669; 4,900,633;4,920,006; 4,938,857; 5,328,768; and 5,492,750, herein incorporated byreference, describe MSVD apparatus and methods to sputter coat metaloxide films on a substrate, including a glass substrate. The MSVDprocess is not generally compatible with providing a PM coating over afloat glass ribbon during its manufacture because, among other things,the MSVD process requires reduced pressure during the sputteringoperation which is difficult to form over a continuous moving floatglass ribbon. However, the MSVD method is acceptable to deposit the PMcoating 24 on substrate 22, e.g., a glass sheet. The substrate 22 can beheated to temperatures in the range of 400° C. (752° F.) to 500° C.(932° F.) so that the MSVD sputtered coating on the substratecrystallizes during deposition process thereby eliminating a subsequentheating operation. Heating the substrate during sputtering is not apreferred method because the additional heating operation duringsputtering can decrease throughput. Alternatively, the sputter coatingcan be crystallized within the MSVD coating apparatus directly andwithout post heat treatment by using a high-energy plasma, but againbecause of its tendency to reduce throughput through an MSVD coater,this is not a preferred method.

An exemplary method to provide a PM coating (especially a PM coating of300 Å or less and having an RMS surface roughness of 2 nm or less) usingthe MSVD method is to sputter a dopant containing coating on thesubstrate, remove the coated substrate from the MSVD coater, andthereafter heat treat the coated substrate to crystallize the sputtercoating. For example, but not limiting to the invention, a target oftitanium metal doped with at least one photoabsorption band shiftingmaterial selected from chromium (Cr), vanadium (V), manganese (Mn),copper (Cu), iron (Fe), magnesium (Mg), scandium (Sc), yttrium (Y),niobium (Nb), molybdenum (Mo), ruthenium (Ru), tungsten (W), silver(Ag), lead (Pb), nickel (Ni), rhenium (Re), and/or mixtures orcombinations thereof can be sputtered in an argon/oxygen atmospherehaving 5-50% oxygen, such as 20% oxygen, at a pressure of 5-10 millitorrto sputter deposit a doped titanium dioxide coating of desired thicknesson the substrate 22. The coating as deposited is not crystallized. Thecoated substrate is removed from the coater and heated to a temperaturein the range of 400° C. (752° F.) to 600° C. (1112° F.) for a timeperiod sufficient to promote formation of the crystalline form oftitanium dioxide to render photoactivity. In one embodiment, thesubstrate is heated for at least an hour at temperature in the range of400° C. (752° F.) to 600° C. (1112° F.). Where the substrate 22 is aglass sheet cut from a float glass ribbon, the PM coating 24 can besputter deposited on the air side and/or the tin side.

The substrate 22 having the PM coating 24 deposited by the CVD, spraypyrolysis or MSVD methods can be subsequently subjected to one or morepost-coating annealing operations. As may be appreciated, the time andtemperatures of the anneal can be affected by several factors, includingthe makeup of substrate 22, the makeup of PM coating 24, the thicknessof the PM coating 24, and whether the PM coating 24 is directly incontact with the substrate 22 or is one layer of a multilayer stack onsubstrate 22.

Whether the PM coating 24 is provided by the CVD process, the spraypyrolysis process, or the MSVD process, where the substrate 22 includessodium ions that can migrate from the substrate 22 into the PM coating24 deposited on the substrate 22, the sodium ions can inhibit or destroythe photoactivity, e.g., photocatalytic activity and/or photoactivehydrophilicity, of the PM coating 24 by forming inactive compounds whileconsuming titanium, e.g., by forming sodium titanates or by causingrecombination of photoexcited charges. Therefore, a sodium ion diffusionbarrier (SIDB) layer can be deposited over the substrate beforedeposition of the PM coating 24. A suitable SIDB layer is discussed indetail in U.S. Pat. No. 6,027,766, herein incorporated by reference.With post-coating heating, a sodium barrier layer for sodium containingsubstrates, such as soda-lime-silica glass, can be utilized. Forapplying the PM coating 24 of the invention in a molten metal bath, thesodium barrier layer is optional.

The SIDB layer can be formed of amorphous or crystalline metal oxidesincluding but not limited to cobalt oxides, chromium oxides and ironoxides, tin oxides, silicon oxides, titanium oxides, zirconium oxides,fluorine-doped tin oxides, aluminum oxides, magnesium oxides, zincoxides, and mixtures thereof. Mixtures include but are not limited tomagnesium/aluminum oxides and zinc/tin oxides. As can be appreciated bythose skilled in the art, the metal oxide can include oxides,super-oxides or sub-oxides of the metal. While the thickness of the SIDBlayer necessary to prevent sodium ion poisoning of the PM coating varieswith several factors including the time period at which a substrate willbe maintained at temperatures above which sodium ion migration occurs,the rate of sodium ion migration from the substrate, the rate of sodiumion migration through the SIDB layer, the thickness of the PM coatingand the degree of photocatalytic activity required for a givenapplication, typically for most applications, the SIDB layer thicknessshould be in the range of at least about 100 Å, such as at least about250 Å, e.g., at least about 500 Å thick to prevent sodium ion poisoningof the PM coating layer. The SIDB layer can be deposited over substrate22 by any conventional method, such as but not limited to CVD, spraypyrolysis, or MSVD methods. Where the spray pyrolysis or CVD methods areemployed, the substrate 22 can be maintained at a temperature of atleast about 400° C. (752° F.) to ensure decomposition of themetal-containing precursor to form the SIDB layer. The SIDB layer can beformed by other methods, including the sol-gel method, which sol-gelmethod as noted above is typically not compatible with the manufactureof a glass float ribbon.

A tin oxide SIDB layer, such as a fluorine doped tin oxide SIDB, can bedeposited on a substrate by spray pyrolysis by forming an aqueoussuspension of dibutyltin difluoride (C₄H₉)₂SnF₂ and water and applyingthe aqueous suspension to the substrate via spray pyrolysis. In general,the aqueous suspension typically contains between 100 to 400 grams ofdibutyltin difluoride per liter of water. Wetting agents can be used assuspension enhancers. During the preparation of the aqueous suspension,the dibutyltin difluoride particles can be milled to an average particlesize of 1 to 10 microns. The aqueous suspension can be vigorouslyagitated to provide a uniform distribution of particles in suspension.The aqueous suspension is delivered by spray pyrolysis to the surface ofa substrate which is at a temperature of at least about 400° C. (752°F.), such as about 500° C. to 700° C. (932° F. to 1292° F.), whereuponthe aqueous suspension pyrolyzes to form a tin oxide SIDB layer. As maybe appreciated, the thickness of SIDB layer formed by this process canbe controlled by, among other parameters, the coating line speed, thedibutyltin difluoride concentration in the aqueous suspension and therate of spraying.

Alternatively the tin oxide SIDB layer can be formed by the CVD methodon the substrate from a metal-containing precursor such as amonobutyltintrichloride vapor (hereinafter “MBTTCL”) in an air carriergas mixed with water vapor. The MBTTCL vapor can be present in aconcentration of at least about 0.5% in the air carrier gas applied oversubstrate while the substrate is at a temperature sufficient to causethe deposition of a tin containing layer e.g. at least about 400° C.(952° F.), such as about 500° C. to 800° C. (932° F. to 1472° F.), toform the tin oxide SIDB layer. As may be appreciated the thickness ofthe SIDB layer formed by this process can be controlled by, among otherparameters, the coating line speed, the concentration of MBTTCL vapor inthe air carrier gas and the rate of carrier gas flow.

An SIDB layer formed by the MSVD process is described in U.S. patentapplication Ser. No. 08/597,543 filed Feb. 1, 1996, entitled “AlkaliMetal Diffusion Barrier Layer”, herein incorporated by reference, whichdiscloses the formation of alkali metal diffusion barriers. The barrierlayer disclosed therein is generally effective at thicknesses of about20 Å to about 180 Å, with effectiveness increasing as the density of thebarrier increases.

The PM coatings 24 of the present invention can be photoactive, e.g.,photocatalytic and/or photoactively hydrophilic, upon exposure toradiation in the ultraviolet range, e.g., 300 nm to 400 nm, and/orvisible range (400 nm to 800 nm) of the electromagnetic spectrum.Sources of ultraviolet radiation include natural sources, e.g., solarradiation, and artificial sources such as a black light or anultraviolet light source such as a UVA-340 light source commerciallyavailable from the Q-Panel Company of Cleveland, Ohio.

As shown in FIG. 1, in addition to the PM coating 24 of the invention,one or more functional coatings 46 can be deposited on or over thesubstrate 22. For example, a functional coating 46 can be deposited overthe major surface 60 of the substrate 22 that is opposite the surface21. As used herein, the term “functional coating” refers to a coatingwhich modifies one or more physical properties of the substrate on whichit is deposited, e.g., optical, thermal, chemical or mechanicalproperties, and is not intended to be removed from the substrate duringsubsequent processing. The functional coating 46 can have one or morefunctional coating films of the same or different composition orfunctionality. As used herein, the terms “layer” or “film” refer to acoating region of a desired or selected coating composition. The filmcan be homogeneous, non-homogeneous, or have a graded compositionalchange. A film is “homogeneous” when the outer surface or portion (i.e.,the surface or portion farthest from the substrate), the inner surfaceor portion (i.e., the surface or portion closest to the substrate) andthe portion between the outer and inner surfaces have substantially thesame composition. A film is “graded” when the film has a substantiallyincreasing fraction of one or more components and a substantiallydecreasing fraction of one or more other components when moving from theinner surface to the outer surface or vice versa. A film is“non-homogeneous” when the film is other than homogeneous or graded. A“coating” is composed of one or more “films”.

The functional coating 46 can be an electrically conductive coating,such as, for example, an electrically conductive heated window coatingas disclosed in U.S. Pat. Nos. 5,653,903 and 5,028,759, or a single-filmor multi-film coating capable of functioning as an antenna. Likewise,the functional coating 46 can be a solar control coating, for example, avisible, infrared or ultraviolet energy reflecting or absorbing coating.Examples of suitable solar control coatings are found, for example, inU.S. Pat. Nos. 4,898,789; 5,821,001; 4,716,086; 4,610,771; 4,902,580;4,716,086; 4,806,220; 4,898,790; 4,834,857; 4,948,677; 5,059,295; and5,028,759, and also in U.S. patent application Ser. No. 09/058,440.Similarly, the functional coating 46 can be a low emissivity coating.“Low emissivity coatings” allow visible wavelength energy, e.g., 400 nmto about 800 nm (e.g., to about 780 nm), to be transmitted through thecoating but reflect longer-wavelength solar infrared energy and/orthermal infrared energy and are typically intended to improve thethermal insulating properties of architectural glazings. By “lowemissivity” is meant emissivity less than 0.4, such as less than 0.3,e.g., less than 0.2. Examples of low emissivity coatings are found, forexample, in U.S. Pat. Nos. 4,952,423 and 4,504,109 and British referenceGB 2,302,102. The functional coating 46 can be a single layer ormultiple layer coating and can comprise one or more metals, non-metals,semi-metals, semiconductors, and/or alloys, compounds, composites,combinations, or blends thereof. For example, the functional coating 46can be a single layer metal oxide coating, a multiple layer metal oxidecoating, a non-metal oxide coating, or a multiple layer coating.

Examples of suitable functional coatings for use with the invention arecommercially available from PPG Industries, Inc. of Pittsburgh, Pa.under the SUNGATE® and SOLARBAN® families of coatings. Such functionalcoatings typically include one or more anti-reflective coating filmscomprising dielectric or anti-reflective materials, such as metal oxidesor oxides of metal alloys, which are preferably transparent orsubstantially transparent to visible light. The functional coating 46can also include infrared reflective films comprising a reflectivemetal, e.g., a noble metal such as gold, copper or silver, orcombinations or alloys thereof, and can further comprise a primer filmor barrier film, such as titanium, as is known in the art, located overand/or under the metal reflective layer.

The functional coating 46 can be deposited in any conventional manner,such as but not limited to magnetron sputter vapor deposition (MSVD),chemical vapor deposition (CVD), spray pyrolysis (i.e., pyrolyticdeposition), atmospheric pressure CVD (APCVD), low-pressure CVD (LPCVD),plasma-enhanced CVD (PEVCD), plasma assisted CVD (PACVD), thermal orelectron-beam evaporation, cathodic arc deposition, plasma spraydeposition, and wet chemical deposition (e.g., sol-gel, mirror silveringetc.). For example, U.S. Pat. Nos. 4,584,206, 4,900,110, and 5,714,199,herein incorporated by reference, disclose methods and apparatus fordepositing a metal containing film on the bottom surface of a glassribbon by chemical vapor deposition. Such a known apparatus can belocated downstream of the molten tin bath in the float glass process toprovide a functional coating on the underside of the glass ribbon, i.e.,the side opposite the PM coating of the invention. Alternatively, one ormore other CVD coaters can be located in the tin bath to deposit afunctional coating either above or below the PM coating 24 on the floatglass ribbon. When the functional coating is applied on the PM coatingside of the substrate, the functional coating can be applied in the tinbath before the PM coating. When the functional coating is on theopposite side 60 from the PM coating, the functional coating can beapplied after the tin bath in the float process as discussed above,e.g., on the tin side of the substrate 22 by CVD or MSVD. In anotherembodiment, the PM coating 24 can be deposited over all or a portion ofthe surface 60 and the functional coating 46 can be deposited over allor a portion of the surface 21.

An exemplary article of manufacture of the invention is shown in FIG. 3in the form of an insulating glass (IG) unit 30. The insulating glassunit has a first pane 32 spaced from a second pane 34 by a spacerassembly (not shown) and held in place by a sealant system to form achamber between the two panes 32, 34. The first pane 32 has a firstsurface 36 (number 1 surface) and a second surface 38 (number 2surface). The second pane 34 has a first surface 40 (number 3 surface)and a second surface 42 (number 4 surface). The first surface 36 can bethe exterior surface of the IG unit, i.e. the surface exposed to theenvironment, and the second surface 42 can be the interior surface, i.e.the surface forming the inside of the structure. Examples of IG unitsare disclosed in U.S. Pat. Nos. 4,193,236; 4,464,874; 5,088,258; and5,106,663, herein incorporated by reference. In one embodiment shown inFIG. 3, the PM coating 24 can be positioned on the number 1 or number 4surfaces, such as on the number 1 surface. The PM coating 24 reducesfogging and makes the IG unit 30 easier to clean and maintain. In thisembodiment, one or more optional functional coatings 46 as describedabove can be deposited over at least a portion of the number 2, number3, or number 4 surfaces.

Advantages of the present invention over the ion-implantation andsol-gel methods of forming self-cleaning coatings include an ability toform a thin, dense, PM film on a substrate as opposed to the generallythicker, porous self-cleaning coatings obtained with theion-implantation and sol-gel coating methods. Still another advantage isthat the method of providing a PM coating according to the presentinvention avoids the need to reheat the substrate after application ofthe coating or coating precursor as is practiced in the conventionalion-implantation and sol-gel methods. Not only does this render thepresent method less costly and more efficient, e.g., less equipmentcosts, less energy costs, and less production time, but also theopportunity for sodium ion migration and in turn sodium ion poisoning ofthe PM coating 24 of the present invention is significantly reduced.Further still, the method of the present invention is easily adapted tothe formation of PM coatings on continuous moving substrates, such as aglass float ribbon.

It will be readily appreciated by those skilled in the art thatmodifications can be made to the invention without departing from theconcepts disclosed in the foregoing description. Accordingly, theparticular embodiments described in detail herein are illustrative onlyand are not limiting to the scope of the invention, which is to be giventhe full breadth of the appended claims and any and all equivalentsthereof.

1. An article comprising: a first substrate spaced from a secondsubstrate, each substrate having an inner surface and an outer surface;and a coating deposited directly on at least a portion of the outersurface of one of the substrates, wherein the coating consistsessentially of titania and at least one additional photoabsorption bandmodifying material selected from vanadium (V), manganese (Mn), magnesium(Mg), scandium (Sc), yttrium (Y), niobium (Nb), molybdenum (Mo),ruthenium (Ru), lead (Pb), nickel (Ni), rhenium (Re), and mixturesthereof, wherein the coating is a substantially non-porous CVD or MSVDcoating; and wherein an outer surface of the coating is exposed to theenvironment.
 2. The article of claim 1, wherein the substrate isselected from glass, plastic, and ceramic.
 3. The article of claim 1,wherein the substrate is selected from annealed glass, tempered glass,and heat strengthened glass.
 4. The article of claim 1, wherein thecoating comprises titania at least partly in the anatase phase.
 5. Thearticle of claim 1, wherein the coating comprises titania at leastpartly in the rutile phase.
 6. The article of claim 1, wherein thecoating has a thickness of about 50 Å to about 2000 Å.
 7. The article ofclaim 1, wherein the substantially non-porous coating is sufficientlydense such that the coating withstands a conventional hydrofluoric testin which a drop of 0.5 weight percent aqueous hydrofluoric acid solutionis placed on the coating and covered with a watch glass for 8 minutes atroom temperature.